Method for performing a pdcch monitoring in a carrier aggregation with at least one scell operating in an unlicensed spectrum and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing a PDCCH monitoring in a carrier aggregation with at least one SCell operating in an unlicensed spectrum, the method comprising: configuring with a first cell group including at least one first cell and a second cell group including at least one second cell served by an eNB; receiving first information for configuring with DRX operation; receiving second information for configuring with additional monitoring period for the second cell group; monitoring a PDCCH signal for a first cell of the first cell group in subframes indicated by the first information; and monitoring a PDCCH signal for a second cell of the second cell group in subframes indicated by the first information and the second information.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for performing a PDCCH monitoring in acarrier aggregation with at least one SCell operating in an unlicensedspectrum and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for performing a PDCCH monitoring in a Carrieraggregation with at least one SCell operating in an unlicensed spectrum.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, the invention is to add anadditional On Duration using in an unlicensed band to common DRXfunction. That can be effect of increasing PDCCH monitoring opportunityin an unlicensed band without any changing of the number of PDCCHmonitoring in the licensed band.

It will be appreciated by persons skilled in the art that the effectsachieved by the present invention are not limited to what has beenparticularly described hereinabove and other advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure;

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios;

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE)

FIG. 9A is an illustration of the CCA check procedure for FBE; and FIG.9B is an illustration of the CCA check and backoff procedures for LBE.

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and 10D is a diagramfor Active State operations for FBE.

FIG. 11 is a diagram for DRX function in a licensed band;

FIG. 12 is a diagram showing a method for a DRX operation in the LTEsystem;

FIG. 13 is a diagram for DRX function with performing LBT procedure in aLAA system; and

FIGS. 14 to 16 are conceptual diagrams for performing a PDCCH monitoringin a carrier aggregation with at least one SCell operating in anunlicensed spectrum according to embodiments of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transceiver (135) and controls it.The apparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 6(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≦N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≦M≦N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios.

Carrier aggregation with at least one SCell operating in the unlicensedspectrum is referred to as Licensed-Assisted Access (LAA). In LAA, theconfigured set of serving cells for a UE therefore always includes atleast one SCell operating in the unlicensed spectrum, also called LAASCell. Unless otherwise specified, LAA SCells act as regular SCells andare limited to downlink transmissions in this release.

If the absence of IEEE802.11n/11ac devices sharing the carrier cannot beguaranteed on a long term basis (e.g., by level of regulation), and forthis release if the maximum number of unlicensed channels that E-UTRANcan simultaneously transmit on is equal to or less than 4, the maximumfrequency separation between any two carrier center frequencies on whichLAA SCell transmissions are performed should be less than or equal to 62MHz. The UE is required to support frequency separation in accordancewith 36.133.

LAA eNB applies Listen-Before-Talk (LBT) before performing atransmission on LAA SCell. When LBT is applied, the transmitter listensto/senses the channel to determine whether the channel is free or busy.If the channel is determined to be free, the transmitter may perform thetransmission; otherwise, it does not perform the transmission. If an LAAeNB uses channel access signals of other technologies for the purpose ofLAA channel access, it shall continue to meet the LAA maximum energydetection threshold requirement. The unlicensed band can be used for aWi-Fi band or a Bluetooth band.

It has been agreed that the LTE CA framework is reused as the baselinefor LAA, and that the unlicensed carrier can only be configured asSCell. The SCell over unlicensed spectrum may be downlink only orbi-directional with DL only scenario being prioritized in the SI. LAAonly applies to the operator deployed small cells. Coexistence and fairsharing with other technologies is an essential requirement for LAA inall regions.

Regarding FIG. 7, LAA targets the carrier aggregation operation in whichone or more low power SCells operate in unlicensed spectrum. LAAdeployment scenarios encompass scenarios with and without macrocoverage, both outdoor and indoor small cell deployments, and bothco-location and non-co-location (with ideal backhaul) between licensedand unlicensed carriers. FIG. 7 shows four LAA deployment scenarios,where the number of licensed carriers and the number of unlicensedcarriers can be one or more. As long as the unlicensed small celloperates in the context of the carrier aggregation, the backhaul betweensmall cells can be ideal or non-ideal. In scenarios where carrieraggregation is operated within the small cell with carriers in both thelicensed and unlicensed bands, the backhaul between macro cell and smallcell can be ideal or non-ideal.

Scenario 1: Carrier aggregation between licensed macro cell (F1) andunlicensed small cell (F3).

Scenario 2: Carrier aggregation between licensed small cell (F2) andunlicensed small cell (F3) without macro cell coverage.

Scenario 3: Licensed macro cell and small cell (F1), with carrieraggregation between licensed small cell (F1) and unlicensed small cell(F3).

Scenario 4: Licensed macro cell (F1), licensed small cell (F2) andunlicensed small cell (F3). In this case, there is Carrier aggregationbetween licensed small cell (F2) and unlicensed small cell (F3). Ifthere is ideal backhaul between macro cell and small cell, there can becarrier aggregation between macro cell (F1), licensed small cell (F2)and unlicensed small cell (F3). If dual connectivity is enabled, therecan be dual connectivity between macro cell and small cell.

In the study to support deployment in unlicensed spectrum for the abovescenarios, CA functionalities are used as a baseline to aggregatePCell/PSCell on licensed carrier and SCell on unlicensed carrier. Whennon-ideal backhaul is applied between a Macro cell and a small cellcluster in the Scenarios 3 and 4, small cell on unlicensed carrier hasto be aggregated with a small cell on licensed carrier in the small cellcluster through ideal backhaul. The focus is to identify the need ofand, if necessary, evaluate needed enhancements to the LTE RAN protocolsapplicable to the carrier aggregation in all the above scenarios.

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE).

The Listen-Before-Talk (LBT) procedure is defined as a mechanism bywhich an equipment applies a clear channel assessment (CCA) check beforeusing the channel. The CCA utilizes at least energy detection todetermine the presence or absence of other signals on a channel in orderto determine if a channel is occupied or clear, respectively. Europeanand Japanese regulations mandate the usage of LBT in the unlicensedbands. Apart from regulatory requirements, carrier sensing via LBT isone way for fair sharing of the unlicensed spectrum and hence it isconsidered to be a vital feature for fair and friendly operation in theunlicensed spectrum in a single global solution framework.

According to ETSI regulation (EN 301 893 V1.7.1) of the Europe, two LBToperations respectively referred to as a FBE (Frame Based Equipment) andan LBE (Load Based Equipment) are shown as an example. The FBEcorresponds to an equipment where the transmit/receive structure is notdirectly demand-driven but has fixed timing and the LBE corresponds toan equipment where the transmit/receive structure is not fixed in timebut demand-driven.

The FBE configures a fixed frame using channel occupancy time (e.g.,1˜10 ms) corresponding to time capable of lasting transmission when acommunication node has succeeded in channel access and an idle periodcorresponding to minimum 5% of the channel occupancy time. CCA isdefined by an operation of monitoring a channel during a CCS slot(minimum 20 μs) at an end part of the idle period.

In this case, a communication node periodically performs the CCA in afixed frame unit. If a channel is in an unoccupied state, thecommunication node transmits data during the channel occupancy time. Ifa channel is in an occupied state, the communication node postpones datatransmission and waits until a CCA slot of a next period.

A CCA (clear channel assessment) check and backoff mechanism are two keycomponents of channel evaluation stage. FIG. 9A illustrates the CCAcheck procedure for FBE, in which no backoff mechanism is needed. FIG.9A illustrates the CCA check and backoff procedure for LBE.

In order to deploy LAA eNB in regions where LBT is required, LAA eNBshall comply with LBT requirements in those regions. In addition, theLBT procedures shall be specified such that fair sharing of theunlicensed spectrum may be achieved between LAA devices themselves andamong LAA and other technologies, e.g. WiFi.

After eNB acquires the unlicensed spectrum through LBT proceduresuccessfully, it may notify its UEs the result so that preparations maybe made accordingly for transmission, e.g., UE may start measurements.

CCA check (FBE and LBE) and backoff mechanism (LBE) are two majorcomponents of LBT operation, and thus are worth further clarification orstudy in order to fulfil LBT requirement efficiently in LAA system.Since the LBT procedure is in preparation for transmitting data orsignals over unlicensed channel, it is straightforward that both MAC andPHY layers are closely involved in the LBT process. FIGS. 10A to 10Dillustrate our views on the interaction and function split between MACand PHY during the CCA check and backoff operations. They can be used tohelp identify the potential impacts that LBT requirements brought toRAN2.

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and 10D is a diagramfor Active State operations for FBE.

An LAA eNB operating status is classified as in either Active State orPassive State, as shown in FIG. 10A.

The passive state means that an LAA eNB has no need of utilizingunlicensed channels, and the active state means that an LAA eNB is inneed of unlicensed resources. The transition from Passive State toActive State is triggered when radio resources over unlicensed channelis needed.

FIG. 10B depicts the operation in Passive State in more details, and isapplicable to both FBE and LBE. The transition from Active State toPassive State occurs when there is no more need of unlicensed channel.

FIG. 10C outlines the operation in Active State, assuming LBE Option Brequirements.

As shown in the FIG. 10C, PHY checks the availability of unlicensedchannel and transmits (steps 1 b, 2 b, 3 b and 6 b), while MAC makes thescheduling decision and decides whether radio resources over unlicensedcarrier is needed (steps 4 b and 7 b). In addition, MAC also generatesbackoff counter N (step 5 b).

It is worth pointing out that scheduling decision in 4 b and 7 bconsiders both licensed and unlicensed channel resources. User data canbe directed for transmission on either licensed or unlicensed channel.When MAC evaluates the demand for unlicensed channel resources (steps 4b and 7 b), it may take PHY's need into consideration, e.g., whether DRSwill be transmitted soon. Step 3 b includes not only the time eNBtransmits data over the unlicensed channel, but also the idle periodthat is required to fulfil LBT requirements, as well as the shortcontrol signalling transmission duration. The initial CCA check (step 2b) is triggered by the demand for unlicensed channel resources, such asMAC data and/or PHY signalling. This is in line with “demand-driven”definition of LBE.

For ECCA check (steps 5 b and 6 b), MAC provides the backoff counter Nand PHY is in charge of starting and performing CCA check in each of theN ECCA slots. The reason of letting MAC but not PHY generate backoffcounter value N is that the MAC scheduler has the betterknowledge/prediction regarding the availability of data that may betransmitted or offloaded over unlicensed carrier(s). In addition, theknowledge of value N will help MAC scheduler predict buffering delay tosome extent. At the end of a failed ECCA and before PHY starts a newround of ECCA, it is reasonable for PHY to check with MAC first whetherthere is still any need to access the resources of unlicensed channel.If MAC scheduler prefers to use licensed carriers for data transmissionsin the next several subframes, or if MAC empties its buffer already,there is no point for PHY to start a new round of ECCA. Because of thenecessity of checking with MAC (step 4 b) and the benefit of MAC knowingN value, it is preferred that MAC provides the backoff counter N to PHY.

FIG. 10D outlines the operation in Active State following FBErequirements. Interpretation of each step is similar to that in FIG.10C.

FIG. 11 is a diagram showing a concept of DRX (Discontinuous Reception).

Referring to FIG. 11, if DRX is set for a UE in RRC_CONNECTED state, theUE attempts to receive a downlink channel, PDCCH, that is, performsPDCCH monitoring only during a predetermined time period, while the UEdoes not perform PDCCH monitoring during the remaining time period. Atime period during which the UE should monitor a PDCCH is referred to as“On Duration”. One On Duration is defined per DRX cycle. That is, a DRXcycle is a repetition period of On Duration.

The UE always monitors a PDCCH during On Duration in one DRX cycle and aDRX cycle determines a period in which On Duration is set. DRX cyclesare classified into a long DRX cycle and a short DRX cycle according tothe periods of the DRX cycles. The long DRX cycle may minimize thebattery consumption of a UE, whereas the short DRX cycle may minimize adata transmission delay.

When the UE receives a PDCCH during On Duration in a DRX cycle, anadditional transmission or a retransmission may take place during a timeperiod other than the On Duration. Therefore, the UE should monitor aPDCCH during a time period other than the On Duration. That is, the UEshould perform PDCCH monitoring during a time period over which aninactivity managing timer, drx-InactivityTimer or a retransmissionmanaging timer, drx-RetransmissionTimer as well as an On Durationmanaging timer, onDurationTimer is running

The value of each of the timers is defined as the number of subframes.The number of subframes is counted until the value of a timer isreached. If the value of the timer is satisfied, the timer expires. Thecurrent LTE standard defines drx-InactivityTimer as a number ofconsecutive PDCCH-subframes after successfully decoding a PDCCHindicating an initial UL or DL user data transmission and definesdrx-RetransmissionTimer as a maximum number of consecutivePDCCH-subframes for as soon as a DL retransmission is expected by theUE.

Additionally, the UE should perform PDCCH monitoring during randomaccess or when the UE transmits a scheduling request and attempts toreceive a UL grant.

A time period during which a UE should perform PDCCH monitoring isreferred to as an Active Time. The Active Time includes On Durationduring which a PDCCH is monitored periodically and a time intervalduring which a PDCCH is monitored upon generation of an event.

More specifically, the Active Time includes the time while (1)onDurationTimer or drx-InactivityTimer or drx-RetransmissionTimer ormac-ContentionResolutionTimer is running, or (2) a Scheduling Request issent on PUCCH and is pending, or (3) an uplink grant for a pending HARQretransmission can occur and there is data in the corresponding HARQbuffer, or (4) a PDCCH indicating a new transmission addressed to theC-RNTI of the UE has not been received after successful reception of aRandom Access Response for the preamble not selected by the UE.

FIG. 12 is a diagram showing a method for a DRX operation in the LTEsystem.

Referring to FIG. 12, the UE may be configured by RRC with a DRXfunctionality and shall perform following operations for each TTI (thatis, each subframe).

If a HARQ RTT (Round Trip Time) Timer expires in this subframe and thedata of the corresponding HARQ process was not successfully decoded, theUE shall start the drx-RetransmissionTimer for the corresponding HARQprocess.

Further, if a DRX Command MAC control element (CE) is received, the UEshall stop onDurationTimer and drx-InactivityTimer. The DRX Command MACCE is a command for shifting to a DRX state, and is identified by a LCID(Logical Channel ID) field of a MAC PDU (Protocol Data Unit) subheader.

Further, in case that drx-InactivityTimer expires or a DRX Command MACCE is received in this subframe, if the Short DRX cycle is configured,the UE shall start or restart drxShortCycleTimer, and use the Short DRXCycle. However, if the Short DRX cycle is not configured, the Long DRXcycle is used. Additionally, if drxShortCycleTimer expires in thissubframe, the Long DRX Cycle is also used.

The UE shall monitor the PDCCH for a PDCCH-subframe during the ActiveTime. If the PDCCH indicates a DL transmission or if a DL assignment hasbeen configured for this subframe, the UE shall start the HARQ RTT Timerfor the corresponding HARQ process and stop the drx-RetransmissionTimerfor the corresponding HARQ process. If the PDCCH indicates a (DL or UL)new transmission, the UE shall start or restart drx-InactivityTimer.

Here, the PDCCH-subframe is defined as a subframe with PDCCH. That is,the PDCCH-subframe is a subframe on which the PDCCH can be transmitted.More specifically, in a FDD (frequency division duplex) system, thePDCCH-subframe represents any subframe. For full-duplex TDD (timedivision duplex) system, the PDCCH-subframe represents the union ofdownlink subframes and subframes including DwPTS of all serving cells,except serving cells that are configured with schedulingCellId (that is,the Scheduled cell). Here, the schedulingCellId indicates an identity ofthe scheduling cell. Further, for half-duplex TDD system, thePDCCH-subframe represents the subframes where the PCell (primary cell)is configured as a downlink subframe or a subframe including DwPTS.

Meanwhile, when not in Active Time, the UE does not perform a SRS(Sounding Reference Signal) transmission and a CSI reporting, which aretriggered by the eNB.

During the above DRX operation, only the HARQ RTT Timer is fixed to 8ms, whereas the eNB indicates the other timer values, onDurationTimer,drx-InactivityTimer, drx-RetransmissionTimer, andmac-ContentionResolutionTimer to the UE by an RRC signal. The eNB alsoindicates a long DRX cycle and a short DRX cycle, which represent theperiod of a DRX cycle, to the UE by an RRC signal.

FIG. 13 is a diagram for DRX function with performing LBT procedure in aLAA system.

In CA, the same DRX operation applies to all configured and activatedserving cells (i.e. identical active time for PDCCH monitoring). Inother words, UE monitors all the component carriers in the same TTIs.When the UE is scheduled on any component carrier, drxInactivityTimer isstarted and that applies to all component carriers. So in other wordsthere is a common DRX applied to all the CCs. LAA is CA based, i.e.licensed band CCs and un-licensed band CCs are served by the same eNB.Thus the common DRX currently used in CA could be seen as the baselinehere, as it is already specified for CA.

In DC, separate DRX configurations can be applied to MCG and SCG, andthe CG specific DRX operation applies to all configured and activatedserving cells in the same CG (i.e. identical active time for PDCCHmonitoring.

However, the difference to CA is that due to Listen-Before-Talk (LBT)there is no guarantee that the channel is obtained for scheduling the UEexactly when desired by the eNB. First the eNB shall do the clearchannel assessment (CCA and subsequently possibly ECCA) on LAA SCell.And only if that succeeds the eNB can start transmitting. The problemwith DRX is that the eNB may not be able to get the channel during UE'sDRX on-duration. This can cause significant delay if the eNB waits untilthe next DRX cycle. And even if CCA succeeds, channel can be kept busyonly a limited time due to LBT requirements. Thus, the DRX configurationshould probably not be very strict for the LAA cells. This means thatthe DRX timers (on-duration, inactivity timer) should be long enough andthe DRX cycle should be short enough to allow more time for gettingaccess to the channel.

So in case DRX timers are not long, scheduling of UE may not besuccessful during the active time and therefore UE will go to DRX sleepbefore eNB has managed to successfully get access to the channel. Thisproblem is illustrated in FIG. 13.

In case common DRX is used, one main problem that arises is that theselonger active times due to LAA SCells would be applied unnecessarilyalso on licensed carriers. This may not allow enough power savingopportunity for the UE in licensed band cells.

Furthermore, the traffic activity could be different in differentcarriers, especially if we have also LAA UL. Therefore also independentDRX for LAA cells could be considered as well. This would be similar towhat we have for DC.

One key question is: how do we ensure UE power saving? Due to LBTrequirements, it seems that common DRX may not be enough to provide UEpower saving. Therefore, we need to ensure a way for UE power saving inLAA e.g. independent DRX.

FIG. 14 is a conceptual diagram for performing a PDCCH monitoring in acarrier aggregation with at least one SCell operating in an unlicensedspectrum according to embodiments of the present invention.

The invention is to use common DRX for both Licensed band (L-band) andUnlicensed band (U-band), but to configure additional PDCCH monitoringperiod for U-band.

The eNB configures the UE with at least one L-band cell and at least oneU-band cell (S1401). That is, the UE performs so called “CarrierAggregation” for the L-band cells and the U-band cells.

The eNB configures the UE with DRX using DRX-Config IE (S1403). TheDRX-Config IE indicates subframes in which the UE has to monitor a PDCCHsignal for the L-band cells and the U-band cells.

The eNB configures the UE with additional PDCCH monitoring period forU-band using U-Band-Monitoring IE (S1405). The PDCCH monitoring periodmay be configured per cell in U-Band. The U-Band-Monitoring period iseither periodic or aperiodic.

The U-Band-Monitoring IE indicates the subframes the UE shall monitorU-Band carriers in addition to DRX on-duration. It may contain Cycle,Offset, and Duration as DRX-Config.

The UE monitors PDCCH on both L-Band cells and U-Band cells inon-duration of DRX (S1407). Additionally, the UE monitors PDCCH only onU-Band cells in U-Band-Monitoring subframes (S1409). In theU-Band-Monitoring subframes the UE does not monitor PDCCH on L-Bandcells. The UE behavior of PDCCH monitoring is shown in FIG. 15A.

When the UE receives a PDCCH indicating UL grant or DL assignment fromU-Band cells in U-Band-Monitoring subframes, the UE keeps monitoringPDCCH on U-Band cells by restarting drx-Inactivity timer. The UEbehavior when a PDCCH indicating UL grant or DL assignment is receivedat U-Band-Monitoring subframe is shown in FIG. 15B.

When the UE receives UL grant or DL assignment from U-Band cells inon-duration of DRX, the UE keeps monitoring PDCCH on both L-Band cellsand U-Band cells by restarting drx-Inactivity timer. The UE behaviorwhen a PDCCH is received from U-Band cells at on-duration of DRX isshown in FIG. 15C.

When the UE receives UL grant or DL assignment from L-Band cells inon-duration of DRX, the UE keeps monitoring PDCCH on both L-Band cellsand U-Band cells by restarting drx-Inactivity timer.

The UE behavior when a PDCCH is received from L-Band cells aton-duration of DRX is shown in FIG. 15D.

FIG. 16 is a conceptual diagram for performing a PDCCH monitoring in acarrier aggregation with at least one SCell operating in an unlicensedspectrum according to embodiments of the present invention.

The invention is to use common DRX for both Licensed band (L-band) andUnlicensed band (U-band), but to configure additional PDCCH monitoringperiod for U-band.

The eNB configures the UE with at least one L-band cell and at least oneU-band cell (S1601). That is, the UE performs so called “CarrierAggregation” for the L-band cells and the U-band cells.

The eNB configures the UE with DRX using DRX-Config IE (S1603). TheDRX-Config IE indicates subframes in which the UE has to monitor a PDCCHsignal for the L-band cells and the U-band cells.

The eNB configures the UE with On-Duration Skip for L-band cells to skipPDCCH monitoring in some of the on duration for L-band cells (S1605).

The On-Duration Skip indicates the subframes the UE shall not monitorL-Band carriers in common DRX on-duration. It may contain Cycle, Offset,and Duration as DRX-Config.

The UE monitors a PDCCH signal for the L-band cells in subframesindicated by the DRX-Config IE, except subframes indicated by theOn-Duration Skip (S1607).

The On-Duration Skip may be configured per cell in L-Band. TheOn-Duration Skip is either periodic or aperiodic.

For example, the UE monitors PDCCH in every 4th On-Duration for L-bandcells, and in every On-Duration for U-band cells.

In summary, in case of an unlicensed band to which an LBT procedure isapplied, it is necessary to frequently have On Duration for trustworthyPDCCH reception. On the contrary, in case of a licensed band, it is notnecessary to have On Duration frequently in the aspect of powerconsumption. In particular, in an LAA situation that the licensed bandand the unlicensed band are aggregated with each other, it may beadvantageous to set DRX configuration different from each other. Thepresent invention has a characteristic of setting additional On Durationfor an unlicensed band only while a common DRX configuration ismaintained. Similarly, the present invention has a characteristic ofsetting skip on duration for a licensed band only while a common DRXconfiguration is maintained. By doing so, it is able to have an effectof increasing a PDCCH monitoring opportunity in an unlicensed bandwithout increasing PDCCH monitoring opportunity in a licensed band.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from essential characteristics of the presentinvention. The above embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims, not by the abovedescription, and all changes coming within the meaning of the appendedclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for a User Equipment (UE) operating in a wirelesscommunication system, the method comprising: configuring with a firstcell group including at least one first cell and a second cell groupincluding at least one second cell served by an e-Node B (eNB) receivingfirst information for configuring with Discontinuous Reception (DRX)operation, wherein the first information indicates subframes in whichthe UE has to monitor a Physical Downlink Control Channel (PDCCH) signalfor the first cell group and the second cell group; receiving secondinformation for configuring with additional monitoring period for thesecond cell group, wherein the second information indicates subframes inwhich the UE has to monitor a PDCCH signal for the second cell group;monitoring a PDCCH signal for a first cell of the first cell group insubframes indicated by the first information; and monitoring a PDCCHsignal for a second cell of the second cell group in subframes indicatedby the first information and the second information.
 2. The methodaccording to claim 1, wherein the second cell group operates in anunlicensed spectrum.
 3. The method according to claim 1, wherein whenthe UE receives a PDCCH indicating uplink grant or downlink assignmentfrom the second cell in subframes indicated by the second information,the UE keeps monitoring a PDCCH signal on the second cell group byrestarting a drx-Inactivity timer and doesn't monitor a PDCCH signal onthe first cell group.
 4. The method according to claim 1, wherein whenthe UE receives a PDCCH indicating uplink grant or downlink assignmentfrom the first cell or the second cell in subframes indicated by thefirst information, the UE keeps monitoring a PDCCH signal on both thefirst cell group and the second cell group by restarting adrx-Inactivity timer.
 5. A method for a User Equipment (UE) operating ina wireless communication system, the method comprising: configuring witha first cell group including at least one first cell and a second cellgroup including at least one second cell served by an e-Node (eNB);receiving first information for configuring with Discontinuous Reception(DRX) operation, wherein the first information indicates subframes inwhich the UE has to monitor a Physical Downlink Control Channel (PDCCH)signal for the first cell group and the second cell group; receivingsecond information for configuring with on-duration skip for the firstcell group, wherein the second information indicates subframes in whichthe UE doesn't monitor a PDCCH signal for the first cell group; andmonitoring a PDCCH signal for a first cell in subframes indicated by thefirst information, except subframes indicated by the second information.6. The method according to claim 5, wherein the second cell groupoperates in a unlicensed spectrum.
 7. The method according to claim 5,wherein when the UE receives a PDCCH indicating uplink grant or downlinkassignment from the second cell in subframes indicated by the secondinformation, the UE keeps monitoring a PDCCH signal on the second cellgroup by restarting a drx-Inactivity timer and doesn't monitor a PDCCHsignal on the first cell group.
 8. The method according to claim 5,wherein when the UE receives a PDCCH indicating uplink grant or downlinkassignment from the first cell or the second cell in subframes indicatedby the first information, the UE keeps monitoring a PDCCH signal on boththe first cell group and the second cell group by restarting adrx-Inactivity timer.
 9. A User Equipment (UE) operating in a wirelesscommunication system, the UE comprising: a Radio Frequency (RF) module;and a processor configured to control the RF module, wherein theprocessor is configured to configure with a first cell group includingat least one first cell and a second cell group including at least onesecond cell served by an e-NodeB (eNB), to receive first information forconfiguring with Discontinuous Reception (DRX) operation, wherein thefirst information indicates subframes in which the UE has to monitor aPDCCH signal for the first cell group and the second cell group, toreceive second information for configuring with additional monitoringperiod for the second cell group, wherein the second informationindicates subframes in which the UE has to monitor a Physical DownlinkControl Channel (PDCCH) signal for the second cell group, to monitor aPDCCH signal for a first cell of the first cell group in subframesindicated by the first information, and to monitor a PDCCH signal for asecond cell of the second cell group in subframes indicated by the firstinformation and the second information.
 10. The UE according to claim 9,wherein the second cell group operates in a unlicensed spectrum.
 11. TheUE according to claim 9, wherein when the UE receives a PDCCH indicatinguplink grant or downlink assignment from the second cell in subframesindicated by the second information, the UE keeps monitoring a PDCCHsignal on the second cell group by restarting a drx-Inactivity timer anddoesn't monitor a PDCCH signal on the first cell group.
 12. The UEaccording to claim 9, wherein when the UE receives a PDCCH indicatinguplink grant or downlink assignment from the first cell or the secondcell in subframes indicated by the first information, the UE keepsmonitoring a PDCCH signal on both the first cell group and the secondcell group by restarting a drx-Inactivity timer.
 13. (canceled) 14.(canceled)
 15. (canceled)
 16. (canceled)